The present invention relates to what is claimed in preambles and is concerned with a position sensitive optoelectronic detector arrangement for the spatial resolution of light beam reception.
Position sensitive optoelectronic detector arrangements are already employed in diverse fields nowadays.
Almost synonymous with this term are lateral effect photodiodes (therefore often also called position sensitive diode/device or PSD for short), which have been part of the prior art for many years. These components consist of a very simple structure of a light sensitive PIN semiconductor diode chip having a resistance layer, which can be used to divide the photocurrent laterally between two (1D PSD) or four (2D-PSD) electrodes at the edge of the chip, depending on the point of incidence of a preferably point light beam. From the ratio of the currents of said electrodes, relatively independently of the signal strength of the light point, the position thereof on the chip can then be deduced. Examples of a 2D PSD are found in (G. P. Petersson and L. E. Lindholm. Position sensitive detector with high linearity. IEEE Journal of Solid State Circuit, SC13(3):392, 1978). An example of a 1D PSD is found in U.S. Pat. No. 5,869,834. Such a 1D PSD is also shown in FIG. 1a (prior art).
Such PSDs are employed e.g. in conjunction with optical lens systems for the non-contact optical determination of a distance to an object by means of laser triangulation or with direct irradiation for high precision alignment of machine beds by means of laser guide beams, etc.
The major advantage of the lateral effect photodiodes stems from the fact that, under optimum boundary conditions and in expedient applications, in some instances extremely high spatial resolutions right down to the μm range can be achieved. The absolute accuracy is considerably poorer, in particular also because the positional accuracy is often dominated by the evaluation electronics connected thereto, the drift effects thereof or extraneous light.
Owing to the usually high sheet resistances, however, such sensors become saturated very early despite biasing with relatively high voltages and are therefore suitable only to a limited extent for being used in direct sunlight without fairly substantial optical filter measures, such as e.g. narrowband dielectric optical bandpass filters.
In order to minimize this problem and in order to further increase the resolution, one dimensional PSDs have been proposed which provide more than two electrodes as taps of the resistance area, which are preferably arranged equidistantly over the detector length. As a result, it is possible, for example, by using four instead of two electrodes, to reduce by a factor of three the internal voltage drops as a result of DC light components at the resistance layer and thus to triple the saturation limit for the same bias voltage. Such an arrangement was proposed in (Huai-Dong Ding and M. Idesawa. Multi-Resolution Image Position Sensing Characteristics of R-HPSD. Journal of Robotics and Mechatronics, 5(2):122-129, 1993) and is illustrated symbolically in FIG. 1b (prior art).
Where laser beams are used for measurement, laser beam receivers are necessary. One typical field of use is for example the reception of laser light from the rotary and linear lasers used on construction sites, in industrial applications and the like. Said lasers emit laser light, for example as a rotating or otherwise moved beam that is punctiform in cross section, as a modulated laser fan that may be spatially static or moved, or as a modulated laser plane that may be fanned out by means of conical mirrors. In order that this radiation can still be used for measurement even at great distances and under unfavorable conditions, special laser beam receivers are needed which take account of the pulse shape of the received light pulses and can differentiate the latter from the ambient light and optical disturbance influences.
Laser beam receivers are often embodied as so called manual receivers for leveling and aligning purposes, sometimes also as machine receivers for fitting to the arms or plates of construction machines for remote display or the automatic control of the position of processing tools e.g. when leveling road surfaces.
What all these laser beam receivers have in common is that they have a linear one dimensionally spatially resolving position sensitive optoelectronic detector arrangement of greater or lesser length which makes it possible to determine the point of incidence of the laser plane or the like thereon and thus to determine and display the position of the laser light receiver in relation to said laser plane in at least one dimension.
Detector arrangements having a length of 50 . . . 120 mm are typically employed in the case of manual receivers, whereas lengths of 120 . . . 1000 mm typically predominate in the case of machine receivers.
Since with traditional lateral effect photodiodes it is largely impossible to fabricate such lengths of the detector arrangements from a single monolithic semiconductor chip, this type of detector arrangement has not found direct commercial application in the case of the laser beam receivers described above.
Rather, in the past attempts have been made, inter alia, to realize alternative position sensitive electro optical detector arrangements which more or less adopt the positive properties of the traditional PSDs by approximating the characteristic thereof by linear arrangements of individual photodiodes and the position dependent bulk resistances thereof by weighting networks, usually chains of e.g. resistances, inductances or resonant circuits. The electrodes of the traditional PSD are then replaced by the ends of the chains and the weighting of the position of the individual photodiode elements is realized by the connection thereof to the corresponding taps (nodes) of the weighting networks. In the literature such arrangements are often referred to as discrete PSD (or D PSD for short), since the position characteristic thereof proves not to be continuous, but rather in discrete steps for very thin light beams, but transitions to quasi continuous profiles for wider beam diameters.
One example thereof is described in (Huai-Dong DING, M. IDESAWA and S. MATSUMOTO. A Comb-Structured PSD and Its Image Position Sensing Characteristics. Journal of the Society of Instrument and Control Engineers, 30(8):883-891, 1994) and is shown in FIG. 1d (prior art) of the present application.
A further discrete PSD was described in (U.S. Pat. No. 7,019,278). Here some of the positive properties from FIG. 1b are transferred into a discrete PSD. The use of more than two taps (output signals) at the weighting networks here likewise has the advantage that voltage drops at the weighting networks as a result of DC light are minimized and that, in the case of more than two taps, it is possible to differentiate between thin beams (useful signal) and rather planar illumination, e.g. as a result of lightning pulses (interference signals).
A further D-PSD was proposed in US 2014/0203172 and is shown in FIG. 1e (prior art). Here two or more D PSDs are arranged in a line. The advantages largely correspond to those in U.S. Pat. No. 7,019,278, but with a disadvantage that a larger number of taps is required and that a continuous transition in the position characteristic between the two D PSDs ranges from difficult to impossible to realize.
A different path was taken in U.S. Pat. No. 9,121,695. This approach is shown symbolically in FIG. 1c. It can be discerned therein that this virtually involves a traditional PSD in accordance with FIG. 1b which has virtually been divided into smaller parts, with the latter being connected again at the adjacent electrodes (multi PSD). What is advantageous over traditional approaches is that this arrangement can consist of a plurality of relatively small PSD chips, which are simpler and thus less expensive to produce and thus also allow detector arrangements of any desired length. For the same properties, however, this arrangement is still very expensive in comparison with other approaches, without having genuine advantages.
All the approaches described up to this point (traditional PSD, D-PSD, Multi-PSD, FIG. 1a to FIG. 10 from the prior art share a common considerable disadvantage by which their applicability to AC applications (pulsed or modulated light beams, pulsed detection events, etc.) in the field of the laser beam receivers mentioned above is made considerably more difficult and their design for applications with high accuracy is made very expensive. The disadvantage can be seen in the fact that the taps of these detector arrangements are electrically connected by the bulk resistances or impedances of the weighting networks and in conjunction with the electrical termination and the junction capacitances of the detector elements over the length of the sensor produce frequency dependent phase shifts and/or frequency dependent amplifications and/or decreases of the position characteristic of the detector arrangement which are in turn still dependent on the temperature. An optimum termination of the taps (outputs) of the detector arrangements by the circuit parts (amplifier stages) connected downstream is ascribed a critical characteristic here since a fluctuation vis à vis temperature or frequency of just a few percent can make a precise position determination impossible. A further disadvantage stems from the fact that the termination impedance of these output signals usually also has to take up the DC currents as a result of DC light. In this case, inductances or their electronic equivalents (NIC, gyrator, etc.) have to be designed such that a fluctuation of the DC current within customary limits (darkness up to full insolation) does not cause an appreciable change in the position characteristic.
High accuracies of the position determination are very difficult to realize here with reasonable costs/low complexity, that is to say that applications with AC light signals such as e.g. the laser light receivers described above can be realized only in a comparatively costly manner.
A different path, one which completely avoids this weighty disadvantage of the stringent requirements made of the termination stages connected downstream, is taken by the optical waveguide PSD disclosed in U.S. Pat. No. 7,394,527 in the name of the applicant (in FIG. 1g therein), since here the position dependent weighting is realized with optical means (optical waveguide with scattering means) and frequency dependent crosstalk between the electrical output signals is virtually completely precluded. However, this approach is also beset by disadvantages. These consist, inter alia, in a wavelength dependence of the position characteristic, which may be up to 2% of the measured position in various commercially conventional laser light sources, and in comparatively high measurement value noise as a result of undesirably inefficient coupling in of the light and a highly position dependent measurement accuracy in conjunction with large light beam diameters, caused by the inherent, tan h( ) position characteristic.
Therefore, a position sensitive optoelectronic detector arrangement which enables high performance but at the same time can be realized cost effectively and which avoids the abovementioned disadvantages of the detector arrangements from the prior art and, when integrated into a laser light receiver, provides for a good cost/performance ratio would be desirable.
Thus, in particular for cost reasons, and for favorable measurement value noise under insolation, it would be desirable to provide a discrete position sensitive optoelectronic detector arrangement.
It would be desirable, in particular, to provide a position sensitive optoelectronic detector arrangement in which the frequency dependent crosstalk between the taps (signal outputs) is largely avoided per se in a wide useful frequency range.
It would also be desirable for the position sensitive optoelectronic detector arrangement not to impose any special requirements in respect of the AC termination of the signal outputs.
It would also be desirable for the position sensitive optoelectronic detector arrangement not to impose any requirements in respect of whether the output signals are processed further as currents or voltages and for the DC currents to be able to be conducted away via separately supplied bias voltages without additional outlay.
It would be desirable, in particular, for the position sensitive optoelectronic detector arrangement to ensure a very good linearity even for very thin light beam profiles and, with large beam profile diameters, not to yield any additional measurement errors over and above the customary secondary problems.
It would likewise be desirable for the position characteristic of the position sensitive optoelectronic detector arrangement to be free of influences of the light wavelength to the greatest possible extent within customary limits of the application.